Apparatus for heat removal by mercury



July 5, 1932. A. J. NERAD APPARATUS FOR HEAT REMOVAL BY MERCURY OriginalFiled Oct. 14, 1927 2 Sheets-Sheet l Ill 2 Inventor; Anthony J. N evacl,

His Attorheg.

July 5, 1932. NERAD 1,866,367

APPARATUS FOR HEAT REMOVAL BY MERCURY Original Filed Oct. 14. 1927 2Sheet-Sheet 2 Inventor: Anthony J. NeY-ad,

by Ma H is Attorney.

Patented July 5, 1932 UNITED STATES PATENT OFFICE ANTHONY J. NERAD, OFSCHENECTADY, NEW YORK, A SSIGNOR '10 GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK APPARATUS FOR HEAT REMOVAL BY MERCURYContinuation of applications Nos. 226,246, flled October 14, 1927, and473,403, filed August 6, 1930. Thifi application filed January 14, 1982.Serial No. 586,637.

This application is a continuation of my application Serial No. 226,246,filed October 14, 1927, and my application Serial No. 473,403, filedAugust 6, 1930, the latter case being a continuation in part of myapplication Serial No. 370,668, filed June 13, 1929.

In connection with apparatus, such as boilers, for vaporizing mercury,it is essential, for known reasons, to reduce to a minimum the amount ofmercury required for operation; In this connection, the difficulty ismet with that while mercury liquid is a fairly good agent for theremoval of heat from a wall with which it is in contact, mercury vaporis a very poor heat-removing agent. As a result, therefore, theapplication of the high temperatures met with in furnaces, to boilertubes containing mercury and exposed directly to the fire, oifersdifli'culties in that if the circulation of the mercury is not main.-tained at a high rate so as to have present liquid mercury for carryingaway the heat, the tubes may be burned and damaged.

The object of my invention is to provide an improved apparatus forheat-removal by mercury, and for a consideration of what I believe to benovel and my invention, attention is directed to the accompanyingdescription and the claims appended thereto.

According to my invention, I provide a mercury vapor generatingapparatus comprising a suitable number of boiler tube units, each boilertube unit comprising a plurality of tubes arranged in spaced relation toeach other through which the mercury circulates in parallel, theplurality of tubes being surrounded by and embedded in a substance which1 term a secondary or heat-transferring substance. The embedded tubes,which may be termed inner tubes, are of comparatively small diameter andconsiderable length so as to offer a relatively large surface for themercury contained therein for the absorption of heat. The secondary orheat-transferring substance receives the heat at an intense rate, itbeing sufiicient in quantity to absorb the heat readily from the firewithout becoming overheated, and distributes it among the inner tubes,the area of the surfaces of the inner tubes being sufiicient to absorbreadily all the heat without being heated to too high a temperature.

The secondary or heat-transferring substance may be any suitablesubstance, either liquid or solid at the operating temperature, whichmeets the requirements.

A specific application of my invention is in connection with wallscreens forfurnaces and it is this application which I have chosen toillustrate and describe.

In the drawings, Fig. 1 is an end view of a furnace wall provided with awall screen embodying my invention; Fig. 2 is a face view, partly insection, of the construction shown in Fig. 1; Fig. 3 is a side view,partly in section and partly broken away, of one of the boiler tubeunits, the same being shown on an enlarged scale; Fig. 4 is a sectionalview taken on line 44, Fig. 3; Fig. 5 is a detail view of amodification; Figs. 6 and 7 are views similar to Figs. 1 and 2 ofanother construction embodying my invention; Fi 8 is a side view, partlyin section and partly roken away, of the upper end of one of the boilertube units shown in Figs. 6 and 7; Fig. 9 is a sectional view taken online 99, Fig. 8; and Fig. 10 is a detail view of the spiral striplocated in the inner tubes.

Referring to Figs. 1 to 4 of the drawings, in which is illustrated anembodiment of my invention wherein the secondary or heattransferringsubstance is liquid at the operating temperature, 1 indicates a furnacewall and 2 indicates generally a wall screen in front of it. The wallscreen comprises a number of boiler tube units, each unit comprising anouter tube 3 in which are arranged a plurality of comparatively smalldiameter inner tubes 4. The lower ends of tubes 4 are fastened into atube sheet 5 which is spaced from the lower end wall 6 of tube 3 anddefines therewith a liquid space 7. The upper ends of tubes 4 arefastened into a tube sheet 8 which is spaced from the upper end wall 9of tube 3 and defines therewith a vapor space 10. There may be severalcircular rows of tubes 4 or there may be only a single circular row asshown. At the center of tube 3 is a rod 11 which forms a filler and fromwhich project at a suitable number of points length a series oiioins 12which serve to space tunes 4i.

Liquid spaces '1 at the flows .s

the direction oi reby acting a means a 3 n d from the vapor,

"1 each tube unit, the

in connection Willi inside the tube 3 surrounding tubes l filled with asui able secondary heat-transliuid 22 *2 lch may be, for example, At 23indicated a filling spout for sad. the secondary in the presentinstance, tubes 3 are shown as being formed in several sections weldedtogeth r is indicated at 24:. The upper ends of the tube structures arebent at an angle, This allows difierential expansion without excessivestress.

At 25 are indicated Walls of refractory material which may be provided,if found desirable, for protecting the upper and lower portions of theboiler tube units from the direct heat of the fire. Walls may besupported in any suitable manner such as from the tube structuresthemselves in the case of the upper wall and from the floor in the caseof the lower wall as is indicated in the drawings.

It is desirable to provide some means for protecting the secondary fluidfrom oxidation, and for this purpose it may provide a suitable hermeticseal for the filling spouts 23, the air from the space above thesecondary liquid being exhausted or not as found desirable. In thepresent instance, I have shown sealing means in the form of plugs 26which fit in the ends of spouts 23.

In operation, the heat from the fire is absorbed by the secondary fluidand is conveyed by it to the mercury in tubes 4.

By reason of the arrangement of a numher of small tubes within a largertube, the tub being in vertical position or arrange with considerableslope, convection currm formed t: the heat is second ill a even-y to onei w one out e, -d in. parallel as re r has the important a to increasethe dcpendabil y or im in operation since the impairment of circu tionin one of the inner tubes of a unit W01 not result in complete failureof the unit fr excessive overheat.

The tube unit arrangement has a further important advantage in that byreason of the arrangement, the resulting stresses on the tubes are low,Thatthe stresses on the tubes be maintained at a low value is im portantsince the tubes are used princn pally where the temperatures are high.which means that the strength of the ma terials is low. In the case ofinner tubes, the static pressure of the molten secondary fluid againstthe outer walls or the inner tubes reduces the eiiective pressure onthem due to the mercury which they contain. On the other hand, the outertube, which is subjected to the most intense heat, has only the staticpressure of the secondary fluid to Withstand, and being tubular and ofrelatively small cross section, the stress is quite low.

The construction of the tube units from an outer tube in whicharearrangcd a number of smaller inner tubes, the tubes beingsubstantially straight and with their axes substantially parallel, hasimportant advantages from a mechanical standpoint in that it results ina construction which can be built at relatively low cost, beingeconomical of both material and labor, and one wherein a tube can bereadily repaired. Also in the case of a structure formed from a numberof tube units, one of the units can be readily replaced.

Most materials suitable as secondary fluids i q in solidify when theunits are allowed to cool. Solidification and melting result incontraction and expansion of the secondary fluid with greatpossibilities of excessive stresses being set up. With my improvedconstruction, such stresses are minimized or eliminated because voidsare formed throughout the tube unit when the fluid solidifies, suchvoids being formed because the cooling surfaces enclose but small crosssections of the solidifying fluid. Also, since, when starting up,circulation of the boiling fluid commences with the application of heat,the hot liquid rises so that the upper parts of the inner tubes reachmelting temperatures of the secondary fluid before much of the lowerregions of the tubes reach such temperatures. As a result, melting ofthe solidified secondary fluid proceeds approximately from the topdownward, thus permitting free expansion of the secondary fluid as themelting proceeds. In this "connection, the arrangement of quite straighttubes with substantially parallel axes is a helpful and importantfeature in that it insures even initial distribution of the heat to thesolidified secondary fluid. Also, in this connection, the baflle plate19 performs an important function in that as the hot liquid mercurybegins to flow upon the application of heat in starting up, the baifleplate directs it downward to the admission ends of conduits 18 so thereis obtained immediately circulation of the hot liquid. At this time thecirculation of the liquid is at relatively low velocity. As theapplication of heat increases, the velocity of the flow in tubes 4increases and as soon as the heating reaches a value such that vapor isformed, the velocity of flow from tubes 4 reaches a value such that thevapor is forced upward by baflle plate 19 to the space above the liquidin drum 16.

Under certain conditions of lesser heat absorption, it may be foundadvantageous for reasons of economy, to group the inner tubes in classrelation to each other and to the outer tube, and under thesecircumstances the convection of the secondary fluid would be reduced.However, the secondary fluid would serve still to provide a good heattransfer bond, although not as good as is obtained when the secondaryfluid surrounds entirely the inner tubes. An arrangement of thischaracter is shown in Fig. 5, wherein 30 indicates the outer tube and 31the inner tubes,

the inner tubes being arranged in contact with each other and with theouter tube. The spaces among the inner tubes are filled with thesecondary fluid. I

Referring now to Figs. 6 to 10, in which is illustrated an embodiment ofmy invention wherein the secondary or heat-transferring substance is asolid at the operatingtemperature, 35 indicates a furnace wall and 36indicates generally a wall screen in front of it.

The wall screen comprises a number of boiler tube units, each unitcomprising an outer tube 37 in which are arranged a plurality ofcomparatively small diameter inner tubes 38. The inner tubes 38 areembedded in a heattransferring substance 39 which is a solid at theintended operating temperature. As the heat-transferring substance,copper, which has a melting point of 1981 F. and a heat conductivityabout nine times that of steel, may be utilized. Or I may utilize alu-=minum which has a melting point of 1216 F. and a heat conductivity aboutfive times that of steel at room temperature but which increases withincrease of temperature, reaching a value about equal to that of copperat high temperatures. At the present time I believe copper to be thebest heat-transferring substance for use in my improved tube. At theends of the tubes are tube sheets 40 provided with openings in which theends of tubes 38 are fastened by suitable means such as welding, andwhichprotect the substance 39 from direct contact with the mercury.Fastened over the ends of the tubes are caps 41 which may bewelded tothe outer tube 37 and which provide upper and lower spaces 42 with whichthe tubes 38 communicate at their upper and lower ends, as shown inlllig.- 8.

Preferably I provide in each inner tube 38 a twisted strip 43 whichserves to give a whirling motion to the mercury flowing upward throughthe tube, causing it to wash the surface of the tube.

The outer and inner tubes may be constructed from steel. For the outertube 1 may use, with advantage, chrome nickel steel I or low carbonsteel, which has been calorized to protect it against oxidation athigher temperatures. The tubes may be constructed in any suitable way.In this connection, however, it is important to have a goodbond be-,tween the tubes and the heat-transferring substance 39 so as to reduceto a minimum the resistance to the flow of heat between the tubes 37 and38 and the substance 39. This is accomplished by uniting the tubes andthe heat-conducting substance by fused metal whereby there is produced,in substance, a unitary metallic structure. By united by fused metal Imean united through the intermediary of'metal which has been fused inthe process of ioining the metals and afterward permitted to hardenwherebv there is formed an intimate bond between the metals to beunited. To this end, in the case of copper, the tubes may be arranged incorrect spaced relation to each other and the copper in molten conditioncaused to flow around the tubes, after which it is permitted to harden.This results in a construction wherein the copper and the tubes areunited by fused metal. In practice, I have found in a conto againseparate the tubes from the copper, the metals being fused together andunited by an autogenous bond.

The spaces 42 at the lower ends of tubes 37 are connected by conduits 44to a supply conduit 45. The spaces 42 at the upper ends of tubes 37 areconnected by conduits 46 to a vapor drum 47 Dotted line A indicates theliquid mercury level in drum 47, and as will be noted from Fig. 6,conduits 46 are connected with drum 47 below the level of the liquidtherein, although they need not be so arranged necessarily. 48 indicatesa conduit through which mercury vapor may be drawn off from drum 47, and49 indicates a supply conduit for liquid mercury. Circulation of liquidfrom drum 47 to supply conduit 45 is effected by a conduit 50 whichconnects the lower portion of drum 47 to conduit 45.

In drum 47 in front of the ends of conduits 46 is a curved baflle plate51 supported by suitable brackets 52. Battle plate 51 stands in spacedrelation to the wall of the drum and extends from a point adjacent tothe bottom of the drum to a point above the liquid level A. There isthus provided beneath the lower edge of baffle plate 51 a passage 53 forthe flow of mercury liquid. In drum 47 is a bafiie 54 provided withopenings 55 through which the vapor flows to conduit 48.

At 56 are indicated walls of refractory material which may be provided,if found desirable, for protecting the upper and lower portions of theboiler tube units from the direct heat to the fire. Walls 56 may besupported in any suitable manner such as from the tube structuresthemselves in the case of the upper wall and from the floor in the caseof the lower wall, as is indicated in the drawlngs.

In operation, the mercury flows from drum 47 down conduit 50 to supplyconduit 45, from which it is fed to the boiler tubes in parallel,flowing upward through all the inner tubes 38 of each boiler tube. Theheat from the fire is absorbed by the solid substance 39 and is conveyedby it to the mercury in the tubes, distributing the heat substantiallyequally among the tubes. The tubes 88 being supplied with mercury attheir lower ends by the vertical or sloping conduit 44, a naturalcirculation of the mercury is set up due to the fact that as the mercuryin tubes 38 is heated, its density is decreased, whereupon it is forcedupward by the mercury of greater density in conduit 50. As a result, noexternal pumping means is required to effect circulation of the mercurythrough tubes 38. This eliminates the unreliability of external pumping.

The use of a substance which is always solid for heat transfer to theinner tubes is of advantage in. that should a crack or hole occur in theouter tube thesolid substance will not run out as would be the case werea assess? liquid heat-transferring substance used. Also since the outertube will be subjected to relatively low stresses, being in substanceonly a covering and protection from chemical attack for theheat-transferring solid, it may be made comparatively thin, or, if thesubstance in which the tubes are embedded is, in itself, suficientlyresistant to the heat of the furnace so it is not afiected adverselythereby, then an outer tube or covering may be dispensed with. Alsoinstead of providing an outer tube ll may treat the outer surface of theheat-transferring solid in a manner to render it capable of operation atthe temperatures to be met with without being alifected adversely by theheat of the furnace.

Use of a substance always solid for heat transfer avoids passing througha change of phase (solidification or melting) and its attendantexpansion problems which are met with where a liquid is used as theheat-transfer medium because most liquids suitable for such purposesolidify when the unit is allowed to cool. By using a substance whichremains solid for heat transfer it is not necessary to provide enoughmercury or boiling fluid so that in starting the boiler, circulationcommences with the application of heat, for some initial heating withoutcirculation will not be detrimental. The increase in volume of mercurydue to boiling may thus be used advantageously with a solid heattransfermedium.

A unit with a solid material as the heattransfer medium is well adaptedto the use of an amalgam as disclosed in my patent No. 1,759,133, datedMay 20, 1930, in place of mercury in the boiler because partialsolidification is likely to occur in the amalgam. This would mean thatcirculation would commence in the unit only after some considerable heathas been applied to the boiler.

The units may be operated in a horizontal position with vapor conduitsvertical, an arrangement such as is found in some of the header and tubearrangements of steam boilers. Circulation in this case may commencewith boiling and it may be arranged to have the liquid flow in onedefinite direction.

As stated above the tube unit arrangement has an important advantage inthat by reason of the use of small tubes the resulting stresses are low.That the stresses on the tubes be maintained at a low value is importantsince the tubes are used principally where the temperatures are high,which means that the strength of the materials is low. In thisconnection I believe that the use of copper as the heat-transferringsubstance possesses especial utility in that it is capable of yieldingor giving slightly, thereby relieving stresses set up in the innertubes.

In accordance with the provision of the Patent Statutes, I havedescribed the prinassess? ciple of operation of my invention, togetherwith apparatus which I now consider to represent the best embodimentsthereof, but ll desire to have it understood that the apparatus shown isonly illustrative and that the invention may be carried out by othermeans.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A heating apparatus comprising a drum and a plurality of tube units,each tube unit comprising an outer tube, a plurality of inner tubes, anda secondary heat-conducting fluid in the outer tube for conveying heatfrom the outer tube to the inner tubes, conduits connecting the innertubes of each tube unit to said drum, and conduit means for conveyingfluid to said inner tubes.

2. A heating apparatus comprising a drum and a plurality of tube units,each tube unit comprising an outer tube, a plurality of inner tubes, asecondary heat-conducting fluid in the outer tube for conveying heatfrom the outer tube to the inner tubes, conduits connecting the upperends of the inner tubes, of each tube unit to said drum, and conduitsfor conveying fluid from said drum to said inner tubes.

3. A heating apparatus comprising a drum and a plurality of tube units,each tube unit comprising an outer tube, a plurality of inner tubes, asecondary heat-conducting substance in the outer tube for conveying heatfrom the outer tube to the inner tubes, conduits connecting the upperends of the inner tubes of each tube unit to said drum, conduit meansfor conveying fluid from said drum to said inner tubes, and means insaid drum for directing fluid from said conduits to said conduit means.

4. A heating apparatus comprising a drum and a plurality of tube units,each tube unit comprising an outer tube, a plurality of inner tubes, asecondary heat-conducting substance in the outer tube for conveying heatfrom the outer tube to the inner tubes, conduits connecting the u perends of the inner tubes of each tube unit to said drum, conduit meansfor conveying fluid from said drums to said inner tubes and a baflleplate in said drum for directing uid from said conduits to said conduitmeans.

5. A heating apparatus comprising a drum and a plurality of tube units,each tube unit comprising an outer tube, a plurality of inner tubes, anda heat-conducting substance in the outer tube for absorbing heat fromthe outer tube and conveying it to the inner tubes conduit meansconnecting the inner tubes of each tube unit to said drum, and conduitmeans for conveying fluid to said inner tubes.

6. Apparatus for generating mercury vapor comprising a drum and aplurality of tube units connected to said drum inparallel, each tubeunit comprising an outer tube, a plurality of inner tubes arrangedtherem,

and a heat-conducting substance in the outer tube for absorbing heatfrom the outer tube and conveying it to the inner tubes, and a means forsupplying mercury to the inner tubes.

7. 'Apparatus for generating mercury vapor comprising a drum and aplurality of tube units connected to said drum in parallel, each tubeunit comprising a comparatively long outer tube, a plurality of innertubes of comparatively small diameter arranged in the outer tube andextending throughout substantially the length of the outer tube, and aheat-conducting substance in the outer tube for absorbing heat from theouter tube and conveyin it to the inner tubes, and means for supp yingmercury to the inner tubes.

8. Apparatus for generating mercury vapor comprising a drum and aplurality of tube units connected to said drum in parallel, each tubeunit comprising an outer tube, a plurality of inner tubes arrangedtherein, and a heat-conducting substance in the outer tube which is asolid at the intended operating temperature for absorbing heat from theouter tube and conveying it to the inner tubes, and means for supplyingmercury to the inner tubes.

9. Apparatus for generating mercury vapor comprising a drum and aplurality of tube units connected to said drum in parallel each tubeunit comprising a plurality 0 tubes arranged in spaced relation to eachother, and a heat-conducting substance which is a solid at the intendedoperating temperature in which said tubes are embedded for absorbingheat and conveying it to said tubes,

and means for supplying mercury to said tubes.

In witness whereof, 'I have hereunto set my hand.

ANTHONY J. NERAD.

